This invention generally relates to airless spray nozzles and more particularly to airless spray nozzle tips.
Further, this invention relates to a method of forming a flat, wide spray pattern of a liquid coating material sprayed at a high flow rate wherein the coating material is evenly distributed across the spray pattern.
Spray nozzles are used to shape and atomize liquids projected from a spray gun. Upon discharge from the spray nozzle, the liquid material breaks up into droplets and forms a spray pattern or cloud of droplets. Various spray patterns are used for different applications. A common spray pattern is the flat fan-shaped pattern.
Nozzles used to produce a flat fan pattern generally take one of two forms, either air or airless. In an airless spray nozzle, the small nozzle orifice, from which the high pressure liquid emerges, shapes the liquid into the fan pattern. The liquid is emitted from the nozzle as a flat sheet or film of material which is caused to break up into droplets by various physical forces acting on the sheet of liquid.
Generally, an airless spray nozzle includes a nozzle tip formed from a blank in which an orifice is cut. One particular airless spray nozzle used in forming a flat spray pattern of atomized liquid is described in Rood U.S. Pat. No. 4,346,849. As disclosed in this patent, an orifice through a nozzle tip is formed by the interpenetration of a first groove on the pressurized or backside of the nozzle tip with a second groove on the discharge side or front side of the nozzle tip. The nozzle tip formed in this fashion produces a predictable fan pattern where the fluid droplets are properly and evenly distributed across the fan pattern. The shape and depth of the interpenetrating grooves determines the spray pattern width and the flow rate of the nozzle tip.
The requirements of a spray pattern formed by an airless spray nozzle in the spray coating industry are stringent. Paint droplets generally must be evenly distributed across the width of the fan pattern. There should be no heavy deposits of coating material made at the extreme edges of the fan pattern. Heaviness at the extreme edges of the fan pattern is known as tailing.
Although nozzles made in accordance with only the disclosure in U.S. Pat. No. 4,346,846 are suitable for use in a wide variety of applications projecting various widths of fan patterns under a wide variety of conditions, but those nozzles are unsuitable for use in producing a a wide spray pattern at an extremely high flow rate. Under these conditions, nozzles made in accordance with the teaching of U.S. Pat. No. 4,346,849 produce relatively heavy tailing.
For purposes of the present invention, a wide spray pattern refers to a pattern which is at least about 26" wide, 10" from the nozzle tip. The spray pattern width, for purposes of the present invention, is defined as the pattern width measured 10" from the nozzle tip when a baked enamel having a viscosity of 21 seconds using a Zahn No. 2 cup at 105.degree. F. is sprayed through the nozzle at about 500 psi and a temperature of about 170.degree. F. The spray pattern width actually formed will vary depending upon the material sprayed and the spray conditions. A high flow rate is generally at least about 0.30 gallons per minute (gpm). Flow rate is defined as the amount of water which will pass through an orifice at 500 psi.
Accordingly, it is an object of the present invention to disclose a spray nozzle which can produce an extremely wide, flat, evenly distributed spray pattern of coating material at a high flow rate. Further, it is an object of the present invention to disclose such a nozzle which is easy to manufacture on a repetitive basis and which provides predictable results.
Further, it is an object of the present invention to provide a method of forming an extremely wide, flat, evenly distributed spray pattern of coating material at a high flow rate.
These, as well as other objects and advantages, can be obtained by using a nozzle which has a nozzle tip having at least two orifices. The orifices are created by the interpenetration of multiple grooves on a single nozzle tip. More specifically, a first groove extends from the back or pressurized side of the nozzle tip. A second and a third groove extend through the front or unpressurized side of the nozzle tip. Each front side groove interpenetrates the backside groove to create orifices. The orifices are provided to form a wide spray pattern. The size of each orifice provides a fraction of the desired flow rate and the combined flow rate of the orifices provides the desired high flow rate.